* Failure to agree in April could trigger trade threats
* Previous law suspended because of international opposition
By Susanna Twidale and Barbara Lewis
LONDON/BRUSSELS, March 13 (Reuters) - A number of EU politicians plan to vote against a deal to exempt long-haul flights from paying for carbon emissions until the end of 2016 in an attempt to prevent the European Union from bowing to international pressure.
The European Parliament's 71-member Environment Committee will vote on March 19 on a deal brokered by EU diplomats earlier in March to extend a so-called "stop the clock" measure exempting intercontinental flights from regulation under its Emissions Trading System (ETS).
Next week's vote of the cross-party committee would be a preliminary indication of whether the proposal can win enough support in the full 766-strong EU Parliament, a step required before it can become law.
Failure to get final agreement on the compromise before the end of April would be likely to reignite tensions with Europe's major trading partners, such as China and the United States, and risk a trade war.
But for environmentalists, it would be a triumph because it would mean that an existing law that requires all aviation to pay for emissions would automatically apply.
Under the "stop-the-clock" proposal, only internal EU flights are charged for emissions.
Matthias Groote, environment committee chairman in the European Parliament, said by phone there was still no majority either way in the committee on the issue.
The centre-right European People's Party (EPP), the biggest grouping in the parliament, is broadly in favour of the extension, but liberal ALDE member Gerben-Jan Gerbrandy said by phone he was encouraging his members to vote against the deal.
Groote said there was still opposition to the deal among some members of his Socialist Party, while the Greens, the European Parliament's fourth-biggest group, have already said they would oppose the proposal.
The European Union in 2012 started charging all airlines that use EU airports for all of their emissions.
But after fierce opposition from China and the United States, it suspended the law to give the U.N.'s global aviation body, the International Civil Aviation Organization (ICAO), more time to craft a global measure to regulate airlines' rising output of heat-trapping gases.
Last October, the roughly 190 nations at ICAO agreed to design a global scheme by 2016, which would not take effect until 2020, and rejected letting Europe apply its own plan to foreign carriers in the meantime.
Gerbrandy said he was seeking a compromise that would mean international airlines would have to pay for their emissions once they entered European airspace, in line with a proposal put forward by the Commission.
"For me this (law) goes much further than aviation and the climate. It is about the position of the EU in the world," he said.
Environmental campaigners also say the parliament should hold out for an airspace approach.
"The International Civil Aviation Organisation recognises that regulating emissions in states' airspace is legal," Bill Hemmings, aviation manager at campaign group Transport & Environment, said. "This is what the parliament should ensure happens now." (editing by Jane Baird)